This application relates to an improved method and apparatus for modifying the shape of the cutting edge of knives and blades to improve their cutting efficiency. The term “knife” or “blade” used herein interchangeably includes a vast array of cutting devices with sharp edges including for example butcher knives, kitchen knives, razors, plane blades, scalpels, chisels, scissors, shears and the like.
Knives and blades are used in a variety of applications for cutting any of a wide range of different materials including vegetables, meats, woven products, cloth, paper products, plastic products and wood products. Most knives are made of metals such as specially hardened steels, however some specialized knives are made of ceramics such as alumina. There are also diamond knives made of single crystal diamonds which because of their ultra strength and hardness can be used to cut and slice harder materials such as metals and selected inorganic crystalline materials, in addition to the softer organic materials.
The vast number of cutting tools are made of metals particularly specialized steels which include carbon to strengthen and increase the durability of the cutting edge together with alloying elements such as molybdenum, vanadium and tantalum, to increase the flexibility and the hardenability of these special steels which generally must be carefully heat treated in order to develop their ultimate strength and flexibility.
The profile of most cutting edges are V-shaped, formed by a series of machining and grinding steps that become more precise in those final steps that create the final edge.
The creation or development of an ultrasharp edge has been the subject of patents by this inventor, including U.S. Pat. Nos. 4,627,194; 4,716,689; 4,807,399; 4,897,965; and 5,005,319 which describe precision mechanical means for abrading an edge with successively finer diamond abrasives and a precision orbital motion to refine the final edge. Further the U.S. Pat. Nos. 5,611,726; 6,012,971; 6,113,476; and 6,267,652B1 by this inventor describe advanced means using a combination of rigid abrasive sharpening elements and unique flexible stropping wheels to form the final ultrasharp edges. Each of these patent references and numerous by others describe successive steps of abrading the edge with finer and finer abrasives to make the final edge as geometrically perfect as possible.
Refinement of the cutting edge by using finer abrasives while sharpening with powered sharpeners or by hand at successively larger edge facet angles will create ultrasharp metal edges, but the perfection of the edge is always limited by the formation of a burr albeit microscopically small along the cutting edge. A burr is formed by the abrasive process as it removes metal along the edge. The very fine edge being created in the final steps can be exceeding by small at its terminus—less than one thousandth of an inch and commonly on the order of a few microns. Such a terminus is exceedingly weak or fragile and it easily bends away from the abrasive as the abrasive attempts to remove more metal in order to form a still finer edge. As more metal is removed—albeit with a relatively low abrading force, that fine edge is bent out of the way in response to the sharpening action of the abrasive—hence creating a burr. Hence the cutting edge is not positioned as a geometric extension of the edge facets but rather is bent over asymmetrically—away from the last abrasive action.
Existence of the bent-over burr destroys the edge geometry and reduces the cutting effectiveness of the edge. When the edge is used for cutting, that burr tends to bend over still further under the forces of cutting and the knife dulls quickly.
The particulate nature of abrasives whether used as loose particles, adhered to a substrate, or on the surface of a bulk abrasive block—(as on an Arkansas stone) tends to create an intermittent burr along the cutting edge. Instead of being a continuously unbroken burr, it tends to be segmented along the edge, broken up into a series of micro burr-like segments along the edge that give the edge a micro serrated characteristic. The smaller the particle size of the final abrasive grit, the smaller the burr is and the smaller are the micro serrated segments.
When cutting smooth non-fibrous vegetables such as tomatoes, cucumbers, and avocados, it is important that any burrs or microserrations along the edge be as small as possible. A knife with very small burrs and microserrations gives a cleaner cut and a better presentation of such food. On the other hand when cutting fibrous foods such as meats, corn, carrots, and baby pumpkins, any microserrations along the edge may aid the cutting process by virtue of a microblade or micro-sawing action that they provide. Because of their minute physical dimensions and broken structure along the edge, such residual imperfections can themselves be very sharp and constitute micro blades that aid in cutting
For an edge to be an effective aid in cutting fibrous materials such as meat, paper products, etc. edge imperfections must not be too large. Further edge imperfection must not be bent too far out of alignment with the edge facets or it will simply bend over quickly when cutting and be ineffective in cutting.